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<html>
  <head>
    <meta charset='utf-8'>
    <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
    <meta name='mobile-web-app-capable' content='yes'>
    <meta name='apple-mobile-web-app-capable' content='yes'>
    <link rel='icon' type='image/png' sizes='32x32' href='favicon-32x32.png'>
    <link rel='icon' type='image/png' sizes='96x96' href='favicon-96x96.png'>
    <link rel='stylesheet' href='css/common.css'>

    <title>Barebones AR</title>
  </head>
  <body>
    <div id="overlay">
      <header>
        <details open>
          <summary>Barebones WebXR DOM Overlay</summary>
          <p>
            This sample demonstrates extremely simple use of an "immersive-ar"
            session with no library dependencies, with an optional DOM overlay.
            It doesn't render anything exciting, just draws a rectangle with a
            slowly changing color to prove it's working.
            <a class="back" href="./index.html">Back</a>
          </p>
          <div id="session-info"></div>
          <div id="pose"></div>
          <div id="warning-zone"></div>
          <button id="xr-button" class="barebones-button" disabled>XR not found</button>
        </details>
      </header>
    </div>
    <main style='text-align: center;'>
      <p>Click 'Enter AR' to see content</p>
    </main>
    <script type="module">
      // XR globals.
      let xrButton = document.getElementById('xr-button');
      let xrSession = null;
      let xrRefSpace = null;

      // WebGL scene globals.
      let gl = null;

      function checkSupportedState() {
        navigator.xr.isSessionSupported('immersive-ar').then((supported) => {
          if (supported) {
            xrButton.innerHTML = 'Enter AR';
          } else {
            xrButton.innerHTML = 'AR not found';
          }

          xrButton.disabled = !supported;
        });
      }

      function initXR() {
        if (!window.isSecureContext) {
          let message = "WebXR unavailable due to insecure context";
          document.getElementById("warning-zone").innerText = message;
        }

        if (navigator.xr) {
          xrButton.addEventListener('click', onButtonClicked);
          navigator.xr.addEventListener('devicechange', checkSupportedState);
          checkSupportedState();
        }
      }

      function onButtonClicked() {
        if (!xrSession) {
            // Ask for an optional DOM Overlay, see https://immersive-web.github.io/dom-overlays/
            navigator.xr.requestSession('immersive-ar', {
                optionalFeatures: ['dom-overlay'],
                domOverlay: {root: document.getElementById('overlay')}
            }).then(onSessionStarted, onRequestSessionError);
        } else {
          xrSession.end();
        }
      }

      function onSessionStarted(session) {
        xrSession = session;
        xrButton.innerHTML = 'Exit AR';

        // Show which type of DOM Overlay got enabled (if any)
        if (session.domOverlayState) {
          document.getElementById('session-info').innerHTML = 'DOM Overlay type: ' + session.domOverlayState.type;
        }

        session.addEventListener('end', onSessionEnded);
        let canvas = document.createElement('canvas');
        gl = canvas.getContext('webgl', {
          xrCompatible: true
        });
        session.updateRenderState({ baseLayer: new XRWebGLLayer(session, gl) });
        session.requestReferenceSpace('local').then((refSpace) => {
          xrRefSpace = refSpace;
          session.requestAnimationFrame(onXRFrame);
        });
      }

      function onRequestSessionError(ex) {
        alert("Failed to start immersive AR session.");
        console.error(ex.message);
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        xrSession = null;
        xrButton.innerHTML = 'Enter AR';
        document.getElementById('session-info').innerHTML = '';
        gl = null;
      }

      function onXRFrame(t, frame) {
        let session = frame.session;
        session.requestAnimationFrame(onXRFrame);

        gl.bindFramebuffer(gl.FRAMEBUFFER, session.renderState.baseLayer.framebuffer);

        // Update the clear color so that we can observe the color in the
        // headset changing over time. Use a scissor rectangle to keep the AR
        // scene visible.
        const width = session.renderState.baseLayer.framebufferWidth;
        const height = session.renderState.baseLayer.framebufferHeight;
        gl.enable(gl.SCISSOR_TEST);
        gl.scissor(width / 4, height / 4, width / 2, height / 2);
        let time = Date.now();
        gl.clearColor(Math.cos(time / 2000), Math.cos(time / 4000), Math.cos(time / 6000), 0.5);
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        let pose = frame.getViewerPose(xrRefSpace);
        if (pose) {
          const p = pose.transform.position;
          document.getElementById('pose').innerText = "Position: " +
            p.x.toFixed(3) + ", " + p.y.toFixed(3) + ", " + p.z.toFixed(3);
        } else {
          document.getElementById('pose').innerText = "Position: (null pose)";
        }
      }

      initXR();
    </script>
  </body>
</html>
